Such continuous torque monitoring is used to detect a possible malfunction of a control unit for an automotive drive or of the automotive drive itself for protecting the occupants of a vehicle as well as outside traffic. If a malfunction is detected, an error response is initiated and the vehicle is converted to a safe vehicle state. For torque monitoring, an admissible total torque is ascertained continuously during operation from a vehicle driver input and is compared with a total actual torque of the drive. In the case of a hybrid drive of an internal combustion engine and an electric drive, the total actual torque is ascertained from the sum of the actual torques of the internal combustion engine and of the electric drive. If the total of the actual torques of the internal combustion engine and of the electric drive exceeds the admissible total torque, an error signal is delivered and the vehicle is converted to a safe vehicle state.
In a gasoline engine, the actual torque of the internal combustion engine is determined from measured values for the air flow rate, the lambda value and the firing angle. For a diesel engine, the actual torque is determined from the fuel pressure, valve opening time and valve closing time as injection parameters. The admissible total torque is determined from the accelerator pedal signal, data from driver assistance systems, gearing data, ESP intervention procedures and torque loss.
To improve functional reliability, the admissible torque and the actual torque of an internal combustion engine are determined by redundantly executed software from redundantly detected input signals of the engine control unit of the internal combustion engine. According to the related art, variables are stored in duplicate, there is a cyclic review of the RAM and ROM memories, and a program sequence control and a command test are provided. Because of extensive monitoring measures, software that allows a rapid program sequence to allow torque monitoring to respond rapidly to malfunctions must be implemented. This is achieved by expressing the variables for the actual torque of the internal combustion engine and for the admissible torque as relative quantities with respect to the maximum possible torque of the internal combustion engine (“standardization torque”). In this way, the ROM code required for torque monitoring is typically reduced by a factor of two to four in comparison with an implementation with absolute torques.
The actual torque of the intrinsically safe electric drive is relayed from its control unit to the engine control unit of the internal combustion engine via a secured communication. In doing so, the value of the setpoint torque of the electric drive is reported together with a diagnostic status to the engine control unit of the internal combustion engine. Since the electric drive is intrinsically safe, the setpoint torque and actual torque are the same, unless the diagnostic status indicates that there is a malfunction in the electric drive.
An object of the present invention is to provide a method which allows simple expansion of torque monitoring for an internal combustion engine to torque monitoring for a hybrid drive.